Service rifle competition, .30 and .223 at 100-600 yards I use 6 o'clock hold (AKA 'pumpkin on a post' or 'dotting the i') for everything. I can't resolve the difference between the black of the front sight and the black of the target sufficiently to use center hold. When I try, I wind up stringing vertically from inconsistency on my hold.

For range changes on High Power, the aiming black circles at 200, 300, and 600 yards are all about 6.5 MOA so the offset from center to six o'clock hold is consistent, i.e. your come-ups will be the same for center or 6-clock hold as long as you don't change sight picture when changing elevation for range.